An air-conditioning apparatus includes, for example, a refrigerant circuit including an outdoor unit being a heat source unit arranged outside a building and an indoor unit arranged inside the building, which are connected to each other by a pipe, and refrigerant circulates through the refrigerant circuit (see, for example, Patent Literatures 1 to 4). Further, in the air-conditioning apparatus, air in a space to be air-conditioned is heated or cooled by using heat rejection from or heat removal by the refrigerant so as to heat or cool the space to be air-conditioned. Here, for example, when the refrigerant is leaked from the indoor unit arranged in an indoor space for some reason, the leakage poses an remarkably serious problem in view of, for example, effects on a human body and safety in a case where the refrigerant is of kind having inflammability, toxicity, or other characteristics. Further, even when the leaked refrigerant is, for example, harmless to the human body, there is a fear in that the refrigerant leaked in the indoor space may increase a concentration of the refrigerant to lower an oxygen concentration in the indoor space to result in adverse effects on the human body. A multi-air-conditioning apparatus including a plurality of the indoor units, in which the pipe configured to connect the outdoor unit and the indoor units ranges up to 100 meters, is filled with a large amount of the refrigerant. Therefore, countermeasures to prevent the leakage of the refrigerant are particularly needed.
Therefore, there has been proposed an air-conditioning apparatus including a refrigerant sensor and a pipe shutoff valve. In the air-conditioning apparatus, when the leakage of the refrigerant is detected by the refrigerant sensor, the leakage of the refrigerant is displayed on a remote controller. In this manner, a person who is present indoors can be informed of the leakage of the refrigerant. Further, when the leakage of the refrigerant is detected, a control unit of the air-conditioning apparatus closes the pipe shutoff valve. As a result, the amount of refrigerant leaked indoors can be reduced.
In Patent Literature 1, there is disclosed an air-conditioning apparatus using carbon dioxide (CO2) as the refrigerant. In Patent Literature 1, when a CO2 sensor installed indoors detects a predetermined amount of CO2, a solenoid valve installed in a gas pipe of the indoor unit is closed, while a solenoid valve configured to control a flow rate of CO2, which is installed in a liquid pipe of the indoor unit, is closed. Further, leakage of CO2 is displayed on a remote controller that is present indoors.
In Patent Literature 2, there is disclosed a multi-air-conditioning apparatus capable of performing a cooling and heating mixed operation. In the cooling and heating mixed operation, when the indoor unit performing a heating operation is stopped, hot gas refrigerant flowing through the indoor unit passes through a flow control valve to return to the indoor unit performing a cooling operation. As a result, the refrigerant is heated to lower cooling capacity in the indoor unit. Patent Literature 2 is intended to solve the problem described above by using the solenoid valve provided in a branch unit at which liquid pipes connected to the plurality of indoor units join together.
In Patent Literature 3, there is disclosed a refrigerant shutoff valve that is available in a fluid circuit in which a fluid flows bi-directionally and is capable of appropriately preventing passage of the fluid in a specific direction. A specific structure thereof is disclosed therein.
In Patent Literature 4, there is described a multi-air-conditioning apparatus including a relay device (branch device) in which the liquid pipes and the gas pipes connected to the plurality of indoor units join together. In Patent Literature 4, the relay device includes shutoff valves provided respectively for the liquid pipes and shutoff valves provided respectively for the gas pipes. Then, by using each of the shutoff valves respectively for the liquid pipe and the gas pipe connected to the indoor unit into which the refrigerant is leaked, the refrigerant is prevented from flowing from an other indoor unit or other units into the indoor unit in which the refrigerant is leaked.